The assignee of the instant application, Paper Machinery Corporation of Milwaukee, Wis. USA is the manufacture of paper cup making machines used to make a variety of cups and containers. A typical cup machine for making paper cups, for instance, includes a turret having a plurality of mandrels about which the containers are formed. The turret sequentially rotates the mandrels into cooperation with a variety of work stations where numerous cup forming procedures occur.
In an exemplary procedure, a circular bottom blank is cut out at one workstation and attached to the end of a mandrel by a vacuum applied through the mandrel. During this procedure, the outside lip of the bottom blank is folded downwardly. At a subsequent workstation, a sidewall blank is wrapped around the mandrel. The sidewall blank is heated and sealed using a seam clamp along an overlapped side seam which runs generally longitudinally along the side of the cup. Typically, a paperboard or solid plastic sheet is coated with a thermoplastic material such as polyethylene, so the bottom and sidewall blanks may be heated and sealed together. In some applications, the sidewall blank includes a flap extending beyond the lip of the bottom blank, and this flap is bent over the lip. At a bottom finishing station, the flap is pressed against the lip from an inside recessed area of the bottom of the cup. By heating the polyethylene and firmly pressing the sidewall flap and the bottom blank lip together, a bottom seal is formed and the cup is provided with a sturdy bottom region having a recessed area. There may also be other worksations where various other additional cup forming procedures are carried out. For example, one station may be used to provide a curl at the top or rim of the cup to provide a more functional drinking container and a better appearance.
At a typical cup bottom finishing workstation, the bottom of the cup is finished by a knurling wheel which squeezes the bottom blank lip between the lower region of the sidewall and the sidewall flap. The knurling wheel is moved forward first into the recessed area on the bottom side of the cup. Then, the knurling wheel is moved laterally and then radially outwardly until it squeezes the sidewall blank, bottom blank lip, and the sidewall flap against an arcuate abutment wall of a bottom sealing clamp or clamp ring which receives the bottom of the cup. Once radially offset, the knurling wheel is rolled about the inside of the arcuate abutment wall until the entire bottom of the cup is pressed together and sealed.
In some bottom finishing stations, the lower flat end of the seam clamp is received in a U-shaped channel formed in the bottom sealing clamp or clamp ring (see FIG. 7A) where the overlapped sidewall seam meets the top of the cup bottom. This creates a common straight line joint between the two clamps at an area designated the channel. Over many years of cup production, the channel area has proven to be the most difficult location on the cup to seal thereby causing tiny leaks at the bottom seal of the cup. Channel area leaks cause cup rejection and high speed paper cup plants leading to production shutdowns which can be expensive. Thousands of cups can be produced before the leakage problem is analyzed or detected. Thus, it would be advantageous to provide cup bottom finishing components, namely, a seam clamp and a bottom seam clamp or clamp ring which eliminate the straight line joint therebetween and improve bottom sealing of the cup.